1. Field of the Invention
The invention relates to novel oil-soluble alkylene glycol esters of partial esters derived from the reaction or organic acid materials such as dicarboxylic acids or anhydrides and an aldehyde/tris-(hydroxymethyl) aminomethane adduct or mixture. These novel oil-soluble alkylene glycol ester derivatives have utility as friction reducing additives for hydrocarbon fuels and lubricating oils.
2. Description of Prior and Related Art
There are two principle environments which are encountered by automotive crankcase lubricants, i.e. cyclical high and low temperatures from stop-and-go driving and continuous high temperatures from extended operation of the automobile over long distances. Each of these environments provokes the presence in the lubricant of varying proportions of foreign particles such as dirt, soot, water and decomposition products resulting from breakdown of the oil. This foreign matter appears responsible for the deposition of a mayonnaise-like sludge which circulates with the oil.
During the past decade, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. One commercial type of ashless dispersant contains nitrogen resulting from the attachment of an amine or polyamine to a long-chain hydrocarbon polymer (the oil solubilizing portion of the molecule), usually polyisobutylene through an acid group, e.g. polyisobutenyl succinic anhydride, by forming amide or imide linkages. Specifically such additives include: (a) lubricating oil detergents of the Schiff base type are prepared by reacting alkenyl succinic acid anhydride and a polyamine to provide an imide intermediate subsequently reacted with an aldehyde (see U.S. Pat. No. 3,455,831); (b) United Kingdom Specificiation No. 809,001 teaches corrosion inhibitors comprising a multiple salt complex derived from the reaction product of hydrocarbyl substituted dicarboxylic acids and hydroxy amines (including 2-amino-2-methyl-1,3-propanediol [AMP] and trishydroxy methylaminomethane (hereafter designated THAM) further complexed with mono- and polycarboxylic acids; (c) U.S. Pat. No. 3,632,511 teaches reacting polyisobutenylsuccinic anhydride with both a polyamine and a polyhydric alcohol including THAM; and, (d) United Kingdom Specification No. 984,409 teaches ashless, amide/imide/ester type lubricant additives prepared by reacting an alkenyl succinic anhydride, with a hydroxy amine including THAM.
In the operation of an internal combustion engine, there are many "Boundary Lubrication" conditions where two rubbing surfaces must be lubricated, or otherwise protected so as to prevent wear and to insure continued movement. Moreover, where, as in most cases, friction between the two surfaces will increase the power required to effect movement and where the movement is an integral part of an energy conversion system, it is most desirable to effect the lubrication in a manner which will minimize this friction and/or reduce wear. As is also well known, both wear and friction can be reduced, with various degrees of success, through the addition of a suitable additive or combination thereof, to a natural or synthetic lubricant. Similarly, continued movement can be insured, again with varying degrees of success, through the addition of one or more appropriate additives.
While there are many known lubricant additives which may be classified as antiwear, antifriction and extreme pressure agents and some may in fact satisfy more than one of these functions as well as provide other useful functions, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
The metal dihydrocarbyl dithiophosphates, e.g. the zinc dialkyl dithiophosphates, are one of the additives which are known to exhibit antioxidant and antiwear properties. While they afford excellent oxidation resistance and exhibit superior antiwear properties, it has heretofore been believed that the same increases or significantly limits their ability to decrease friction between moving surfaces. As a result, compositions containing zinc dialkyl dithiophosphates were not believed to provide the most desirable lubricity and, in turn, it was believed that use of compositions containing the same would lead to significant energy losses in overcoming friction even when antifriction agents are included in the composition.
Known ways to solve the problem of energy losses due to high friction in crankcase lubrication include the use of synthetic ester base oils which are expensive and the use of insoluble molybdenum sulfide and graphite dispersions which have the disadvantage of giving the oil composition a black or hazy appearance.